HA! Ok, I have managed to tweak the .dat file in my SH4 install (keeping a backup of the original of course) and when I play in a type 7B, both gyrocompasses on the bridge now function correctly!
my do I feel smug now. Now if only I could remember exactly what I did....
[edit] just to avoid confusion I have deleted part of this post, as I am learning and now realise that half of what I had originally thought and written was not at all true.
Before I can post these files though I'd better speak to Lurker, as the files I'm tweaking come straight from his superb OpMonsun mod, maybe he can just incorporate them in a patch or something - I mean I can't really take credit for polishing somebody elses creation can I! also I will have to get the original files tweaked not my already modded versions as well as look through the other sub types and fix any others that need it... I shall start tomorrow though this could be my first contribution to subsim. give me a week or so I'll see how much work there is to do.